The present invention relates to an articulated arm to be lowered under a slab, through an opening in the latter, in order to carry and guide a device or an instrument of any type whatsoever under the slab and laterally to the opening.
It can be applied to taking samples of nuclear waste emptied into special vertical cylindrical tanks, closed at the top by a concrete slab acting as biological protection and pierced by a single central opening, with a small surface area and whose cover is then removed. The sampling procedures existing at present, among which one can mention the use of long rods introduced obliquely into the opening, are not convenient and hardly allow the point of sampling to be chosen with precision. The articulated arm described herein offers, on the other hand, the possibility of easy samplings even at the periphery of the tank, furthest away from the opening, with the advantage that the sampling equipment can be set with great precision and without the need for any delicate or tiring manoeuvring. It is evident that the invention can be applied to other equipment apart from sampling tools, and in particular sensors or measuring equipment.
In its most general form, the invention relates to an articulated arm to be lowered into an opening in a slab acting as cover for a tank, comprising an upper section and a lower section linked together by an articulation, a means of control of an angle formed by the sections, a bearing placed around the opening and comprising a fixed ring integral with the slab and a turning ring integral with the upper section, a means of control for rotating the turning ring, and a tool suspended from the lower section by a cable of variable length.
Thus, a combined movement of rotation of the whole of the arm around the fixed ring and pivoting of the lower section makes it possible to place the free end of the lower section under the desired point of the slab; it then suffices to lower the tool to give it the right height and reach the surface of the waste to be sampled.
In addition, the lower section is formed of two articulated parts, a return pulley is set at the articulation between the sections, a suspension pulley is set at the free end of the lower section and the suspension cable of the tool, which moreover extends above the slab and the arm, passes under the return pulley and over the suspension pulley.
Certain measures, for perfecting the invention, make it possible to maintain an almost perfect seal despite the necessary movements of the arm, to assemble and disassemble the arm quickly and to control the different movements with precision.
The American patent 4 805 650 describes an articulated arm lowered through the opening of the cover of a container and turning to orient an instrument for projecting water in the container; in addition, the instrument can be lowered by releasing its suspension cable.
Nonetheless, it is not indicated whether or not this arm has means for adjusting the angle of the sections at will, in order to carry the end of the tool to a desired radial position, since the lower section remains in a horizontal position resting on a stop, so that the instrument remains close to the wall of the container to be cleaned.
An improvement proposed here consists of designing the lower section of the arm in two parts articulated together. The assembly of the arm on the opening of the slab is thus simplified, since the lower section remains folded against the upper section, taking less space. When the arm has been fixed on the turning ring of the bearing, the lower section is lowered by passing it through the opening in the slab, which is possible since it has not yet been extended; the assembly of the arm is completed by prolonging and locking the two parts of the lower section in the tank. The arm thus passes from a folded state in which it can be easily installed to an extended state where the lower section is long and offers great possibility of access to all positions in the tank. Such a procedure for extension and locking can be accomplished in particular if the parts of the lower section are articulated by an axle situated on their front edges in a direction for pivoting the lower section relative to the upper section, the means of control of the angle formed by the sections comprising a reversible drive, allowing the lower section to be pivoted in two opposite directions, and the parts of the lower section comprising locking means on their rear edges.
The locking means can in particular comprise axles on a first of the sections, notches on the other one of the sections, springs making the axles protrude from the first of the sections towards the other of the sections, and a cable able to be tightened to make the axles fit into the first of the sections.